1. Field of the Invention
The present invention relates to a Peltier cooler serving as an electronics cooling device and to a semiconductor laser module using the Peltier cooler.
2. Description of the Related Art
A semiconductor laser module is used to convert an electric signal to an optical signal in, for example, an optical fiber transmission. By driving a semiconductor laser device provided within the semiconductor laser module by an electric signal, a modulated signal light is obtained. Since the oscillation wavelength and optical output of the semiconductor laser has a temperature dependency characteristics, it is required to control the temperature of the semiconductor laser to ensure stable operation. To this end, a semiconductor laser module including a Peltier cooler serving as an electronics cooling device has been developed.
As an example of the laser module including the Peltier cooler, a module disclosed in the lecture theses C-180 of the Autumn Convention for the Electronics, Information and Communications Society in 1993 is known.
The module disclosed therein, however, has a problem that creep tends to occur in a fixed portion using a low temperature solder and that the optical system cannot be maintained in an optimum state for a long time.
To solve this problem, Japanese Patent Application Unexamined Publication No. 2-66987 discloses a semiconductor laser module wherein a cooling device is provided in a module package and a cylindrical laser unit having such characteristics that the optical axis is less shifted by changes in outside temperature, is fixed by a solder. Important elements of the optical module are provided in this cylindrical laser unit, thereby disregarding time series shifts in the optical axis.
According to the above-described conventional semiconductor laser module, a cylindrical laser unit is housed in the module and the shape of the module is thereby limited. As a result, the conventional module has disadvantages in that it is difficult to have versatility, manufacturing costs are increased and that the structure becomes complex.
According to a semiconductor laser module disclosed in Japanese Patent Application Unexamined Publication No. 1-220491, a Peltier cooler is provided between a laser module having a semiconductor laser, optical components and the like mounted on a carrier substrate, and the inner base of the module package. According to a semiconductor laser module disclosed in Japanese Patent Application Unexamined Publication No. 1-86260, a module package has double bases, a laser unit is fixed on the upper base and a Peltier cooler is fixed on the lower base. In the latter case, too, the above-mentioned problem remains unsolved since the laser unit and the Peltier cooler are fixed by a low temperature solder.
Meanwhile, according to a semiconductor laser module disclosed in Japanese Patent Application Unexamined Publication No. 4-355706, a metal pattern is formed on an upper surface insulating board to thereby fix a semiconductor laser, optical components and the like by means of YAG laser. However, in this case, it is necessary to fix the components while aligning the optical axis on the insulating board within a module package, which is quite different from the original laser unit manufacturing assembly. As a result, a lot of constraints arise.